The majority of the energy consumed by society is produced from fossil fuels. In order to meet the continuing and expanding use of petroleum, it is necessary to upgrade the lower quality crude oils, which exhibit a progressive decrease in API gravity and a rise in sulfur content. However, it is equally necessary to remove sulfur from oil to meet the strict new environmental regulations which have been enacted.
The commercial hydrodesulfurization (HDS) process which is currently used to remove sulfur from petroleum employs Co—Mo/Al2O3 or Ni—Mo/Al2O3 catalysts. While HDS and its modified versions, e.g. modifying the catalyst activity or reactor configuration, etc. are highly efficient in removing thiols, sulfides, and disulfides, it is however, less effective in removing refractory sulfur present in aromatic sulfur compounds, e.g. dibenzothiophene, and their alkylated derivatives. In addition, the HDS process has high operating costs due to the high pressure and high temperature employed and the extensive use of hydrogen gas. Therefore, achieving a viable and economical desulfurization process is a major challenge to the oil industry. Furthermore, with the increase in oil prices, the development of new technologies and processes for desulfurization of heavy oil, at a lower cost, have taken on even greater importance.
In U.S. Pat. No. 6,274,026, Schucker et al. discloses a technology based on the polymerization of sulfur compounds in an electrochemical cell using ionic liquids as electrolytes. However, it is not efficient due to the difficulty in separating the polymerized compounds.
In U.S. Pat. No. 7,001,504, Schoonover discloses a method to extract organosulfur compounds from hydrocarbons using ionic liquids. Due to the high price and the difficulty to recycle these ionic liquids, commercialization of this method is a challenging task.
US Published Application No. 2008/0257785 to Varma et al. discloses a sorbent for the adsorption of aromatic sulfur compounds from liquid fuels. Such sorbents cannot, however, be used for heavy oil feeds like VR or crude oils.
U.S. Pat. No. 4,670,113 to Lewis, discloses electrochemical activation in gasification and a combined gasification liquification process due to the production of reactive atomic hydrogen from dissociated water. However, catalytic electrodes and the application to desulfurization are not disclosed.
U.S. Pat. No. 4,954,229 to Kim et al. discloses a bioelectrochemical process for removing sulfur compounds from fuels using hydrogen and bacterium to reduce sulfur compounds and produce hydrogen sulfide. However, the low conversion using anaerobic bacterium makes the deployment of this invention impractical.
The electrochemical generation of hydrogen is disclosed by Pintauro in U.S. Pat. No. 6,218,556 for hydrogenating unsaturated fatty acids, constituents of an edible or non-edible oils triglycerides using solid polymer electrolyte. However, there is no disclosure of using a solid polymer electrolyte for desulfurization due to the relatively high operating temperature and the fouling of the polymer which is encountered when using heavy oil feeds.
Baez et al. in U.S. Pat. No. 7,244,351 and US Published Application No. 2008/0251422 disclose the removal of sulfur from hydrocarbon feeds using two compartments separated by a metal membrane in a cell. Although promising results (˜35% sulfur reduction) were obtained for a model sulfur compound (thiophene), only ˜13% reduction was obtained for diesel oil. Furthermore, the process is not practical for processing heavier oil feedstocks due to membrane fouling and diffusion limitations.
Currently, water electrolysis for hydrogen production is more costly when compared to the large-scale chemical process which is based on the steam reforming of natural gas (methane). However, an appreciable increase in water electrolysis is expected in the future as natural gas resources diminish and the production of cheap electrical power in nuclear power plants increases. Also, photovoltaic devices can be used as an alternative green source of electrical energy.